To scale down the size of semiconductor devices requires establishing a viable fabrication technique for dealing with the levels of dimensions below deep submicrons. For example, the production of 256-Mb DRAM's necessitates fabricating contact holes as small as 0.2 .mu.m in diameter and 2 .mu.m in depth. To establish the fabrication technique of this magnitude of precision requires providing techniques for evaluating the precision of what is fabricated. Of such evaluation techniques, what is particularly in demand is one for analyzing qualitatively and quantitatively any residues that remain on the surface of wafers after dry etching. In analyzing such residues, it should be noted that the wafer surface is not necessarily flat; areas with large ups and downs symbolized by the contact holes above also need to be analyzed.
Heretofore, the analysis of residues over appreciably undulating areas has been generally carried out by cutting the fabricated wafer and by observing the cross section thereof using a scanning electron microscope (SEM). This method has a number of disadvantages. One disadvantage of the method is that it is simply for observing the shape of the residues and not for identifying them. Another disadvantage is that, the observed wafer cannot be returned whole into the fabrication process. A further disadvantage is that the conventional method is not fit for observing residues on the order of several nanometers. When the development of Gb-order semiconductor integrated circuit devices is concerned, the above-mentioned disadvantages are critical in that they can significantly degrade yield and analysis accuracy.
One conventional method that bypasses the need to cut the wafer for observation is the so-called fluorescence X-ray analysis. Japanese Patent Laid-Open No. 243855/1988 discloses an example of this method in the form of an analyzing apparatus using charged particles. The disclosed apparatus irradiates an electron beam to a sample and observes fluorescence X-rays emitted therefrom. The observation of fluorescence X-rays involves the use of crystals arranged at 22 degrees with respect to the center axis of the electron beam irradiated.
In analyzing residues qualitatively and quantitatively using fluorescence X-rays, what matters is where to locate means for observing the X-rays. That is, it is necessary to avoid the absorption of the fluorescence X-rays emitted from the sample by locating the observation means so that the position from which the X-rays emanate will be observed directly. However, there have been no definite criteria for locating the means for observing fluorescence X-rays, with little attention paid thereto. Illustratively, whereas the above-mentioned analyzing apparatus using charged particles has its crystals arranged at 22 degrees relative to the center axis of the generated electron beam, the angular arrangement is not fully capable of avoiding the absorption of the fluorescence X-rays emitted from the sample. In particular, the above analyzing apparatus is incapable of addressing DRAM's of 4 Mb or greater in capacity, the mainstay of semiconductor devices from now on, in analyzing qualitatively and quantitatively the surface residues of their samples.